The present invention relates to a simple, one-step process for the preparation of nitroolefins by thermal dehydration of vicinal nitroalcohols.
Nitroolefins have been prepared by various methods known in the art. For example, U.S. Pat. No. 4,384,149 teaches a process for the preparation of one nitroalkene by the reaction of one alkene with dinitrogen tetraoxide in the presence of oxygen and an ether solvent to form an alkene-dinitrogen tetraoxide adduct and subsequent reaction of this adduct with sodium fluoride in the presence of an inert gas. Another method is to contact olefins with nitric oxide in the presence of an ether solvent as taught by U.S. Pat. No. 3,658,922.
Thermal dehydration of aryl nitroalcohols at high temperatures is known to produce nitroolefins in high yields. However, similar attempts to thermally dehydrate alkyl or alkyl-substituted nitro alcohols have not resulted in the production of the desired nitroolefin but, instead, provides various condensation products. To avoid these unfavorable reaction conditions, U.S. Pat. No. 2,414,594, and USSR Pat. Nos. 125,250 and 154,253 teach that the nitroolefin can be produced by the initial formation of a nitroacetate which can generate the nitroolefin through the elimination of acetic acid. An alternative method is to employ the use of catalysts. For example, U.S. Pat. Nos. 3,240,823 and 3,510,531, teach the use of alumina as a catalyst for the dehydration of nitroalcohols to the corresponding nitroolefin at temperatures between 50.degree. and 150.degree. C.
An object of this invention is to provide a new and improved process for the production of various types of nitroolefins. A further object is to provide a simple, one-step process for the production of nitroolefins without the requirement of catalysts.
The above objects are accomplished, as evidenced by the present invention without the need of catalysts nor a multistep process as, for example, initially forming nitroacetates from nitroalcohols with subsequent removal of acetic acid.